The spin wave scattering from the quasi-two dimensional antiferromagnet NiPS3

NiPS3 is a quasi-two-dimensional material with the Ni2+ forming a honeycomb structure in crystallographic planes that are weakly bound by van der Waals forces. It is similar to graphite in this regard although, unlike graphite, it is magnetic, and hence it is of great interest to the graphene community. Recent neutron spectroscopy measurements show a remarkable ungapped Y-shaped dispersion of the spin waves that extend up to 55 meV. The low energy excitations are narrow in Q both in and normal to the planes. This type of excitation is highly unexpected for a two-dimensional material, which should only have very weak dispersion normal to the planes, and is reminiscent of gapped Y-shaped dispersion in Hg-based superconductors. We wish to use MERLIN with rep-rate multiplication to measure simultaneously the low and high energy spin waves, and thus to parameterise the Hamiltonian.NiPS₃是一种准二维材料（quasi-two-dimensional material），其中Ni²⁺在由范德瓦尔斯力（van der Waals forces）弱耦合的晶面内构筑了蜂窝状晶格结构。该材料的这一结构特性与石墨类似，但与石墨不同的是，它具有本征磁性，因此受到石墨烯研究领域的高度关注。近期的中子光谱学（neutron spectroscopy）测量结果显示，其自旋波（spin waves）呈现出显著的无隙Y型色散关系，色散范围最高可达55 meV。无论是沿晶面方向还是垂直于晶面的方向，该材料的低能激发在倒易空间动量矢量Q中均表现出窄化特征。这类激发模式对于二维材料而言极为反常——常规二维材料在垂直于晶面方向的色散本应极弱——该现象却让人联想到汞基超导体（Hg-based superconductors）中的有隙Y型色散关系。本研究拟采用搭载重复率倍增系统的MERLIN中子谱仪，同时测量低能与高能自旋波，进而完成哈密顿量（Hamiltonian）的参数化表征。